This invention concerns a method to dismantle the sort of batteries with an enclosed cell which is protected by a plastic case. More specifically, it concerns a method to process nonaqueous solvent-type batteries which contain in their electrolytes, salts comprising cations and Lewis acid ions. This method is a safe and efficient way to process used lithium batteries which contain lithium hexafluorophosphate in their electrolytes.
For our purposes a nonaqueous solvent-type battery is a secondary battery which uses a nonaqueous solvent in its electrolytic solution and a light metal such as lithium in its cathode.
A nonaqueous solvent is any solvent other than water. The term is not limited in meaning to simple solvents other than water, but also includes mixtures of solvents.
Recent concerns over the trend toward global warming have resulted in a call for more efficient use of electric power in order to avoid further proliferation of thermal generating plants. One way in which power might be used more efficiently would be to normalize power use by temporarily storing excess power at night and releasing it during the daytime. To bring this about, we must realize secondary batteries capable of storing such power. Concerns over air pollution, too, have led to a call for the development of large secondary batteries which can serve as the power supply for an automobile.
The demand for smaller secondary batteries has also been increasing yearly, both for their usefulness as backup batteries in computers and word processors and for their role as power supplies in small home appliances. In particular, the popularization of portable appliances and the improvement of their capabilities have produced a greater demand for small secondary batteries. With this expanding demand for batteries has come a serious concern that the chemical substances which make up the batteries be used efficiently and that measures be taken to prevent used batteries from posing an environmental hazard.
The sort of batteries now in demand are high-performance secondary batteries with capabilities equal to those of the appliances in which they are used. The most prominent examples of these to have been developed for the market are lithium ion batteries, which use an intercalation complex in which lithium ions have been embedded as the active material of their positive electrode and graphite as the active material of their negative electrode. Lithium, transition metals and other valuable substances which can be reused can be found in the lithium ion batteries. However, these batteries also contain extremely reactive substances like alkaline metals, which are used as the active material for their negative electrode, as well as electrolytes which contain substances likely to react with water.
Thus when we dismantle nonaqueous solvent-type batteries like lithium ion batteries, we must safely deactivate their active substances, including their active materials and their electrolyte solution, and at the same time safely and effectively recover any valuable materials which can be reused.
However, metallic lithium (which reacts with water to produce hydrogen) and organic solvents are used in the construction of lithium ion batteries, and they contain numerous other combustible compounds; so it is extremely difficult to recover valuable materials such as lithium cobalt oxide from these batteries.
In schemes disclosed in Japanese Patent Publications (Kokai) 6-346160 and 7-245126 to recover valuable materials including cobalt (actually, lithium cobalt oxide) from used lithium secondary batteries, the used battery is heated and crushed. The crushed materials are passed through a sieve and then separated by a magnet.
In Japanese Patent Publication 7-207359, the used lithium secondary battery is burned in a primary combustion process at 350 to 1000xc2x0 C. It is then crushed and the resulting fragments are passed through a sieve and subjected to a secondary combustion process. The fired fragments are treated with an acid, the pH is adjusted to between 4 and 5.5 by an oxidizing gas which is blown into the acid, and the solution is filtered. An alkali is added to the filtrate, and the valuable materials are recovered from the resulting precipitate.
However, lithium ion batteries which are enclosed cells are enclosed in a protective plastic case. Their constituent materials, which include the active material in the negative electrode, the separator, the active material in the positive electrode, the electrolyte solution and the collector, are enclosed in a protective stainless or other type of steel case. If, using one of the techniques discussed above, a used lithium secondary battery of this sort is heated to between 350 and 1000xc2x0 C. in a primary combustion process, the heat of combustion will cause the lithium cobalt oxide in the enclosed cell to decompose and emit oxygen. At the same time, the volatile (and flammable) solvent in the electrolyte solution will vaporize. The pressure of the vaporization may cause the cell case to burst open, in which case the vaporized and combustible organic solvent and oxygen will ignite. If the solvent and oxygen experience a sudden pressure spike while the case is still intact, they may even explode.
In Japanese Patent Publication 6-251805, a device such as a water jet is used to cut apart or make a hole in the case of a lithium battery. The lithium is processed by reacting it with water or some other reactant. The lithium, the hydrogen which is the other product of the reaction and the electrolyte solution are recovered. There is no combustion to cause a fire, and the materials are recovered safely and efficiently. To minimize combustion with the hydrogen when the battery case is cut open, the process is carried out in an atmosphere of inert gas. However, the use of a water jet requires that it be performed at normal temperatures. If any of the jet is at a lower temperature, and the battery is not fully discharged, the reactive lithium remaining in it will react violently with the moisture component in the air, producing combustible hydrogen gas, as will be discussed shortly.
In Japanese Patent Publication 6-3338352, three processes are used. In Process 1, the negative electrode containing lithium is exposed. In Process 2, the electrolyte is separated from the battery. In Process 3, to prevent a large quantity of hydrogen from being generated when the lithium and water or alcohol come in contact, the surface of the negative electrode which contains the lithium is treated with a solvent such as alcohol or water. Once this is completed, the inside of the negative electrode is also treated with a solvent.
In the prior art techniques described above, the process by which the negative electrode containing lithium is exposed consists of crushing the battery with a hammer crusher, a diamond cutter or a cutter-mixer. When the plastic and metal cases of a number of enclosed cells are cut open simultaneously as described above, the residue of the plastic cases sticks to the crushed fragments of the metal cell cases, and it is very difficult to remove. In addition, when a lithium ion battery which is not fully discharged is crushed, a short circuit will be created when its positive and negative electrodes come in contact with each other. The short circuit will generate Joule heat, causing the temperature inside the battery to rise. The lithium cobalt oxide comprising the positive electrode will decompose, producing oxygen. At the same time, the volatile (and flammable) solvent in the electrolyte solution will vaporize. If a spark is produced when the case is cut, the vaporized combustible organic solvent and the oxygen can ignite; or, if the pressure in the battery spikes abruptly, they can explode.
Another shortcoming of the prior art techniques described above is that a two-step treatment is required to prevent a large quantity of hydrogen from being generated when the lithium and water or alcohol come in contact. In order to execute the two-step process, the composition and quantity of the processing liquid must be controlled while the volume of hydrogen being produced is monitored. Controlling these variables is a complicated matter and does not solve the fundamental problem, which is the production of hydrogen.
We shall now discuss, from the viewpoint of difficulties experienced in the prior art, the configuration and basic problems of lithium ion batteries, since they are the kind of battery which this invention regards as most likely to be broken down so that their materials can be recycled.
Lithium ion batteries of the type described above comprise a number of cylindrical or rectangular enclosed cells (each a discrete battery) and a plastic case wrapped in wire which serves to connect the cells electrically to their control board. The plastic case makes up 20% of the weight of the battery unit.
Each enclosed cell consists of a positive electrode, a positive collector which is coated with the positive electrode, a negative electrode, a negative collector which is coated with the negative electrode a separator which is placed between the collectors, and a cell housing.
A thin sheet of a material such as aluminum foil is used as the positive collector; a thin sheet of a material such as copper foil is used as the negative collector.
The active material of the positive electrode consists of a simple or composite substance or a surface-active agent which is a complex metal oxide containing lithium. This complex metal oxide consists of a lithium ion such as lithium cobalt oxide and a specified metal.
The positive electrode is formed by coating the positive collector, a sheet of aluminum foil, with the active material. This material may be a substance to enhance electron conduction (a conductive substance) such as acetylene black adjusted by polyviridene chloride and n-methylviridone, a solvent.
The active material of the negative electrode is a substance which can take up and release lithium. Metallic lithium and lithium compounds are commonly used; however, lithium alloys and other materials are also found in these lithium compounds.
In addition to lithium alloys, other compounds which contain lithium include carbon materials with a structure of disordered layers and graphite. Even materials which do not contain lithium initially may be used as the negative electrode. In this case, lithium is produced in the material by an electrochemical process.
The negative electrode is formed by coating the copper foil which serves as the negative collector with an active material comprising a polyviridene chloride binder and a coating adjusted with n-methylpyloridone, a solvent.
The electrolyte solution may comprise a simple solvent such as ethylene carbonate, diethylene carbonate, dimethylcarbonate or diethyl ether, or it may be a composite of two or more solvents. If the latter, it may be an organic electrolyte solution in which one or more fluorine compounds such as lithium phosphohexafluoride (LiPF6) are dissolved.
For the separator, a porous resin film such as porous polypropylene film is used.
In the enclosed cell, the eddy structure which is created by interposing a separator between a positive electrode and a negative electrode, both of which are formed into sheets as described above, is enclosed not only by the organic electrolyte solution, but also by a cell housing comprising nickel-plated or stainless steel sheeting. Generally a safety valve is provided in the cell housing to prevent the cell from exploding when its internal pressure increases.
In addition to the primary lithium batteries discussed above, secondary batteries with a non-aqueous electrolyte have been developed which use metallic lithium in their negative electrode. However, the metallic lithium used in the negative electrode forms dendrites when the battery is repeatedly charged and discharged. This causes contact short circuits between the poles and shortens the life of the battery. Recently, to address this problem, non-aqueous electrolyte secondary batteries have been proposed which use carbonaceous substances as the active material in their negative electrode. In this case oxides of lithium compounds would be used as the active material in the positive electrode, so we could expect a safe and long-lasting battery with high energy density.
Because lithium ion batteries of the sort discussed above contain active substances and electrolyte solutions which are unstable when they interact with air, water or high temperatures, the following problems must be considered when such batteries are processed.
(1) Inside the used battery but outside the sealed cell are one or more plastic casings which protect the cell. These casings contribute 20% of the battery""s weight. When recovering cobalt, the faster it is removed from the system, the greater the economy which is realized.
(2) If, for example, an undischarged lithium ion battery which uses lithium cobalt oxide as its positive electrode is crushed at normal temperature, its positive and negative electrodes will come into contact, causing a short-circuit current to flow. This current will generate Joule heat, and the temperature inside the battery will rise.
(3) When the temperature in the battery rises, the lithium cobalt oxide constituting its positive electrode will break down, releasing oxygen. At the same time, the volatile (i.e., flammable) solvent in the electrolyte solution will vaporize.
Furthermore, the vaporized combustible organic solvents and oxygen may be ignited by sparks produced when the battery is cut into, or the battery may explode due to the precipitous increase in its internal pressure. Even a discharged battery can ignite in this way causing a fire to occur.
(4) The activated lithium in an undischarged lithium ion battery will react vigorously with moisture in the air, releasing combustible hydrogen gas. This reaction can occur even in a discharged battery with the same result: combustible hydrogen gas will be released.
(5) The fluorine compounds in hexafluorophosphate lithium used as an electrolyte may react with moisture in the air, producing dangerous gases such as pentafluorophosphate and hydrogen fluoride. In the simple or compound solvent serving as the electrolyte in the lithium ion battery, which may comprise one or more of ethylene carbonate, diethylene carbonate, dimethylcarbonate or diethyl ether, an organic electrolyte is used in which one or more fluorine compounds such as lithium phosphohexafluoride (LiPF6) are dissolved. The fluorine compound serving as the electrolyte, which may be lithium phosphohexafluoride,may react with moisture in the air to produce hydrogen fluoride, a harmful gas. Another fluoride compound which may produce noxious gases is arsenic phosphohexafluoride, which may produce arsenic fluoride or hydrogen fluoride. Such reactions may also occur in discharged nonaqueous solvent-type batteries, producing pentafluorophosphate, pentafluoroarsenic, or hydrogen fluoride.
(6) Lithium ion batteries have an electrolyte between a positive electrode comprising aluminum foil coated with lithium cobalt oxide and a negative electrode comprising copper foil, the collector, coated with graphite. The separator consists of polypropylene and polyethylene. The container which serves as the cell housing is made of copper or aluminum. When the battery is processed, all of these constituent materials must be separated and recovered in a reusable form. Among the more valuable of these materials, the most difficult to separate and recover are the lithium cobalt oxide which is coated onto the aluminum in the positive electrode and the copper which is coated with graphite in the negative electrode.
(7) In the secondary batteries used in laptops and cell phones (hereafter, we shall use the term xe2x80x9cbattery packxe2x80x9d for a battery enclosed in a plastic case and the term xe2x80x9cbattery cellxe2x80x9d for one or more enclosed cells inside a plastic case), the plastic case which surrounds the sealed battery cell represents 20% of the total weight of the battery. As we have already mentioned, when recovering cobalt, the faster it is removed from the system, the greater the economy which is realized. However, as we shall discuss shortly, in the prior art a hammer crusher, a diamond cutter or a cutter-mixer was used to crush the plastic case and expose the sealed battery cell. When the battery was crushed, the residue of the plastic case would stick to the crushed fragments of the cell case, and it was very difficult to remove. In addition, when the battery cell was crushed in a subsequent process, the fragments of the case would bring the positive and negative electrodes in contact with each other, causing a short-circuit current to flow. This would cause the internal pressure in the cell to spike suddenly, possibly resulting in an explosion.
If the battery pack were combusted in order to burn off its plastic outer case, the combustion heat would break down the lithium cobalt oxide in its sealed cell and produce oxygen. At the same time, the volatile (flammable) solvent in the electrolyte solution would vaporize, and the vaporized and combustible organic solvent and oxygen would ignite, or if the internal pressure in the battery rose suddenly, they might even explode.
Thus it proved difficult using prior art techniques to crush the plastic case and sealed battery cell safely and efficiently, no matter whether the battery was crushed at ambient temperature or combusted.
In the forthcoming-technique described in WO 94/2517, a battery pack is separated into plastic case and battery cell by immersing the pack in a liquid nitrogen bath and reducing its temperature to approximately xe2x88x92100xc2x0 C. It is then shocked once with an energy equivalent to that experienced in a fall from a height of 5 to 20 meters. More specifically, a rotor is used which has a rotary force of 700 to 900 rpm. This rotor, which has a scoop on it, accelerates the battery pack and causes it to collide with the wall of the tower. This breaks open the plastic case and releases the sealed battery cell.
However, it is difficult to apply in a stable fashion a single shock which delivers 100 J/kg to 600 J/kg of energy. As a result, this prior art technique is of limited application.
A technique which is similar to the prior art techniques and to that of this invention is disclosed in Patent Publication 10-241748. However, this prior art technique does not employ freezing to separate the sealed battery cell from its plastic case, but rather entails freezing a sealed battery cell with a safety valve once the plastic case has been removed. Its objective is thus different from that of the current invention.
The objective of this invention is to provide a safe and efficient process by which used lithium ion batteries could be dismantled. More specifically, the first objective is to remove from the system safely, certainly and as swiftly as possible the plastic case which encloses a sealed battery cell.
A second objective is to prevent a short circuit from occurring when a lithium ion battery is broken open in order to prevent accidents caused by excessive current flowing in the short circuit between the positive and negative electrodes.
A third objective is to prevent oxygen from being generated by the breakdown of cobalt lithium oxide, the material of the positive electrode, when the temperature spikes suddenly, and to prevent the volatile solvent in the electrolyte solution which is generated from vaporizing.
A fourth objective is to prevent the reactive lithium remaining in the lithium battery from reacting with the moisture component of the atmospheric air to produce combustible hydrogen gas.
A fifth objective is to prevent harmful gases from being produced by the reaction of fluorine compounds such as lithium phosphohexafluoride, an electrolyte, with the moisture component of the atmospheric air.
A sixth objective is dismantle the battery in such a way that the electrolyte, the solvent containing it and the solid materials can be separated completely from the crushed mixture.
With respect to a seventh objective, the solvent system and the system to process the solids must be two separate processing systems. Here the objective in separating the of solids is to remove the poisonous fluorine compounds and flammable solvent so that the solids could be broken down without having to consider possible dangerous interactions.
An eighth objective is to provide a processing method which would recover cobalt lithium oxide move efficiently and which would result in the recovered cobalt lithium oxide being more nearly pure.
A ninth objective is to provide a method to dismantle batteries containing salts composed of cations and Lewis acid ions, in particular lithium ion batteries, safely and efficiently. More specifically, it is the object to provide a method by which the lithium ion batteries could be processed safely. This method would prevent harmful gases from being generated from fluorine compounds such as lithium phosphohexafluoride which are used as electrolytes.
As will be made clear in the description of the invention and the explanation of the embodiments which follows, another objective of this invention was to provide a safe and efficient method to process lithium ion batteries in particular, since they contain a number of separable and recoverable materials of value, including lithium cobalt oxide, an oxide of a compound of lithium and a transition metal, aluminum and copper.
We shall next discuss the configuration of this invention.
This invention comprises a method to process a battery pack (hereafter, xe2x80x9cbatteryxe2x80x9d) in which one or more sealed batteries (hereafter, xe2x80x9cbattery cellsxe2x80x9d) are enclosed within a plastic case. It is distinguished by the fact that it comprises two processes. In the first, the battery is cooled to a temperature no greater than xe2x88x9250xc2x0 C. and repeatedly subjected to vibration and pressure by a number of objects whose rigidity and specific gravity are greater than those of the plastic. In this way the battery is separated into a sealed battery cell and a plastic case. In the second process, the sealed battery cell separated in the process is heated to a temperature of at least 200xc2x0 C. in a non-oxidizing atmosphere to separate mainly the organic materials.
As was explained in our discussion of the prior art, it is difficult to apply in a stable fashion a shock energy of 100 to 600 J/kg which is delivered in a single shock. Instead, the battery is repeatedly vibrated or squeezed to separate the plastic case from the sealed battery cell.
To be more specific, in the process to separate the case from the cell, the battery is cooled to a temperature no greater than xe2x88x9250xc2x0 C., combined with a number of objects of greater rigidity and specific gravity than the plastic, and subjected to vibration. The vibration may be low-frequency vibration provided, for example, by a ball vibration device. In this case, the ball applying the vibration should have a volume ratio between 0.2 and 1 of that of the battery cell.
The process to separate the case from the cell might alternatively comprise cooling the battery to a temperature no greater than xe2x88x9250xc2x0 C. and subjecting it to pressure and vibration provided by a number of objects of greater rigidity and specific gravity than the plastic. In this way the plastic case will be broken open and separated from the battery cell. More specifically, the objects which exert pressure upon the battery should be rods (including hollow rods) having a round, elliptical or square cross section, which are chilled to a temperature no greater than xe2x88x9250xc2x0 C. and rotated. The vibration which these rods impart to the rotary space should be low frequency vibration.
This invention is applicable to a method of processing batteries comprising a sealed battery cell which is protected by a plastic case. It is by no means limited in its application to lithium ion batteries or batteries with non-aqueous solvents only.
If the case of a sealed battery cell is composed of a magnetic material, the plastic case may be separated from the sealed cell magnetically. If the case is composed of another material, for example aluminum, the case and cell may be separated using the difference in specific gravity between the two or by means of a sieve, whichever is convenient.
We shall now discuss the second objective of this invention.
As was discussed earlier, the positive collector in a lithium ion battery is made of a thin sheet of material such as aluminum foil, and the negative collector is made of a thin sheet of material such as copper foil.
When a battery cell containing these substances is combusted in an atmosphere of air, the aluminum of the positive electrode and the copper of the negative electrode within the cell are oxidized and become aluminum oxide and copper oxide. Because the oxidized aluminum and copper are brittle, particles of these substances will come away when the particles of lithium cobalt oxide which are stuck to the foil serving as a positive collector are peeled away. These particles of aluminum and copper oxide contaminate the cobalt lithium oxide which is recovered, adversely affecting the purity of the recovered product.
In Japanese Patent 10-241748, a technique is disclosed by which the sealed battery cell is crushed while its temperature is maintained below the melting point of the electrolyte solution.
In this prior art technique, when the sealed battery cell is chilled and crushed, the following problems are observed.
(1) Sealed battery cells contain polyethylene or polypropylene separators which constitute approximately 0.2 of their comparative weight. In order to deal with these substances efficiently in a later process, a large volume of equipment is required.
(2) It is difficult to completely separate metal components from polyethylene or polypropylene resin components simply by chilling and crushing the battery.
The second process of the present invention, then, is to heat the sealed battery cell separated from its case in the first process to a temperature of at least 200xc2x0 C. in a non-oxidizing atmosphere while employing a safety valve on the cell. This will serve to separate mainly the organic materials from the rest of the battery.
To completely remove the organic resin component, the battery should be heated to a temperature of at least 500xc2x0 C. To minimize the presence of dioxins in the exhaust gas, it should be heated to a temperature of at least 800xc2x0 C.
The non-oxidizing atmosphere may be either a vacuum or an atmosphere of inert gases.
With this invention, as can be seen in FIG. 1 or FIG. 7, the sealed battery cell is heated to at least 200xc2x0 C. in a vacuum or an atmosphere of inert gases. The material constituting the separator, whether polypropylene or polyethylene, the lithium phosphohexafluoride used as the electrolyte, and the ethylene carbonate, diethylene carbonate, dimethyl carbonate or diethyl ether used as the solvent, that is to say, all the organic solvents and organic resins, will undergo pyrolysis. The products of this pyrolysis will escape and be dispersed upward through the safety valve of the battery cell. The gases dispersed at this time will contain combustible organic solvents which can easily ignite; however, the vacuum or atmosphere of inert gases lacks any hydrogen to ignite the solvents or cause them to explode if there is a sudden increase in the internal pressure of the battery.
Such an atmosphere will also prevent any reactive lithium remaining in an undischarged lithium ion battery from reacting.
Furthermore, the aluminum foil coated with lithium cobalt oxide which serves as the positive electrode and the copper foil coated with graphite which serves as the negative electrode will also have no opportunity to oxidize. Since the aluminum and copper foil in the battery cell will not be oxidized, they will not become brittle. When the particles of lithium cobalt oxide which are stuck to the aluminum foil are peeled off, the aluminum will not flake away, but will remain in the state of foil or metallic elements (even if in a molten state). This greatly facilitates the recovery of lithium cobalt oxide and enhances the purity of the recovered product.
In other words, one of the distinctive features of this invention is that when the non-oxidizing atmosphere is a vacuum, the organic materials, such as the products of pyrolysis of the organic solvents and resins separated by heating the battery, are recovered by cooling the battery.
Another distinctive feature of this invention is that when the oxidizing atmosphere consists of an inert gas such as nitrogen, helium, argon, or neon, the liquid or solid organic materials, which remain when the gaseous materials are separated by heating the battery, are heated to decompose in an atmosphere of inert gases or other non-oxidizing gases.
The invention disclosed in claim 5 of this application is the method by which the battery is dismantled, given in the order in which the processes are executed.
This method is distinguished by the fact that it entails the following: a process in which the battery is broken open to separate the sealed battery cell from its plastic case; a process in which mainly the organic materials are separated from the sealed battery cell after the cell has been removed from its case in the preceding process; and one or more processes in which the useless materials are removed and the targeted valuable materials are separated in an orderly fashion from the crushed fragments produced in the crushing process.
The invention disclosed in claim 6 of this application is distinguished by the fact that ultrasonic or ball vibration is employed to peel the active materials of the positive (or negative) electrode off the metal foil.
The invention disclosed in claim 7 of this application is distinguished by the fact that the active materials of the positive (or negative) electrode are peeled off the metal foil by a stripping agent or by a combination of the stripping agent and a means of inducing vibration.
In the invention disclosed in claim 8 of this application, the active materials of the positive (or negative) electrode are separated from the metal foil by dissolving the foil in a strongly acidic or alkaline solution.
The valuable lithium cobalt oxide and spheroidal graphite are separated from the metal foil, whether aluminum or copper, by the means. However, because the lithium cobalt oxide and spheroidal graphite are in the form of microscopic particles, their subsequent handling in order to achieve combustion is problematical.
For this reason the current invention provides that after the particulate substances from the active materials of the positive and negative electrodes are separated from the metal foil and passed through a sieve, they undergo size enlargement.
With this invention, the particles of the lithium cobalt oxide and spheroidal graphite are formed into units resembling charcoal briquets to facilitate their subsequent combustion.
The combustion, of course, is not compulsory. As is disclosed in claim 15 of this application, the particulate matter containing the metal foil and the active material of the positive or negative electrode may be separated by passing it through a sieve. The material recovered from the sieve may then be separated by sedimentation so that the carbon may be removed and the lithium cobalt oxide recovered.
In this case, it is useful to include a process in which the suspended carbon is removed from the water remaining from the sedimentation process. It may be that among the substances recovered by the sedimentation process there is an ion solution of either fluoride or phosphate ions. In this case, once the carbon has been removed by a suspension process, as will be discussed shortly, a fixative such as calcium hydroxide should be added to the ion solution to fix those ions.
The processing system for the solid materials, namely the aluminum or copper foil and the resins containing valuable materials such as lithium cobalt oxide and spheroidal graphite, must be entirely separate from the processing system for the solvent. In particular, when processing the solid materials, the harmful fluorine compounds in the electrolyte and the flammable solvent must first be removed so that the solids can be broken down without having to worry about the influence of potentially dangerous components.
With this invention, the process in which the targeted valuable materials are separated should entail a subprocess in which the lithium hexafluorophosphate, a harmful substance, is dissolved in an aqueous solution. The lithium hexafluorophosphate dissolved in the aqueous solution should be fixed as will be described shortly.
That is to say, it is a distinctive feature of this invention that the lithium hexafluorophosphate separated in the specified process is broken down into fluoride and phosphate ions through the mediation of a heated acidic aqueous solution. The ions in the solution are then fixed by adding a fixative such as calcium hydroxide to the solution.
In the prior art techniques disclosed in Japanese Patent Publications 6-346160 and 7-245126, valuable materials such as lithium cobalt phosphate are recovered from used lithium secondary batteries as follows. The used lithium secondary battery is combusted and then crushed. The crushed fragments are separated by a sieve, and lithium cobalt phosphate is recovered below the sieve. Because the particles of lithium cobalt phosphate are of such small diameter, however, they tend to adhere to the impurities which remain in the sieve, resulting in incomplete recovery when a sieve is the only means of separation.
To address this problem, the current invention features the following process. The resin component is removed from the battery by a heating process, and the remaining materials are washed in water. The active material of the positive or negative electrode, which consists of microscopic particles of lithium cobalt oxide, is dispersed in the water and then recovered from this dispersed state.
Another distinctive feature of the current invention is that the ion-rich gas is not fixed via the wet process, but by a dry process such as one involving a bag filter. More specifically, the harmful materials such as lithium hexafluorophosphate are broken down in the heating process into an ion-rich gas containing fluorine and phosphate ions. The ion-rich gas is fixed by a dry process in which it is forced into contact with a fixative such as powdered calcium hydroxide. This is a sub-process of the process by which the targeted valuable materials are separated from the worthless materials.
Because this invention entails a dry process such as bag filtration, it simplifies the handling of the materials and allows a smaller volume of equipment to be used.
In the process to separate the targeted valuable materials, this invention allows the iron component to be removed magnetically once the particulate mixture containing the metal foil and the active material of the positive or negative electrode has been separated by a sieve.
With this invention, the addition of the magnetic separation process allows us to remove any iron which may be intermixed with the recovered material and so obtain a lithium cobalt oxide which is more nearly pure.
There are some applications which require that the recovered lithium cobalt oxide contain iron. In such cases, the magnetic separation process can be omitted.
In the invention we have been discussing, the lithium hexafluorophosphate solution resulting from heating the battery, processing the exhaust gases and then separating the components by immersing them in a water bath produces a stable aqueous solution. To be more specific, because the materials remain stable in solution without being ionized, we cannot produce a stable CaF2 and Ca3(PO4)2 by adding calcium hydroxide Ca(OH)2 to the solution. In other words, we cannot fix the ions.
If we add acid to the lithium hexafluorophosphate solution, thereby maintaining the acidity of the aqueous solution, we can investigate accelerating the decomposition as in Formula 1 below (hydrolysis). However, even if we add the acid at ambient temperature or increase the concentration of the acid, it is clear that the decomposition (i.e., hydrolysis) can scarcely be accelerated. And using a more concentrated acid causes problems with respect to corrosion of the equipment and safety.
LiPF6+5H2Oxe2x86x92LiOH+HF+PO(OH)3xe2x80x83xe2x80x831)
The results of various investigations led the present inventors to believe that by heating the acid, or to be more specific, by using an acid solution which has been heated to between 65 and 100xc2x0 C. (i.e., to a temperature at which it will not boil) we can accelerate the (hydrolytic) decomposition substantially.
The acid used in this invention must have a higher ionic strength than the acid produced by the hydrolysis (according to Formula 1, HF (hydrogen fluoride)). FIG. 17 shows a graph reproduced from The Handbook of Chemistry, Fourth Revised Version of the Basic Edition, Part II (Compiled by the Chemical Society of Japan), page 323, which gives the relationship between the concentration of an acid solution and its ionic strength. From the graph we can see that acids with a higher ionic strength than HF include HClO4, HCl and H2SO4. If the HF is of a lower concentration, HNO3 will be included in this range as well.
With these acids, even a dilute solution will have a higher ionic strength than HF, and hydrolysis as in the Formula 1 will be effectively accelerated.
By adding calcium hydroxide Ca(OH)2 to the solution once the hydrolysis has been effected, we can produce a stable CaF2 and Ca3(PO4)2 as in Formulas 2 and 3.
Ca(OH)2+HFxe2x86x92CaF2+2H2Oxe2x80x83xe2x80x832)
3Ca(OH)2+2PO(OH)3xe2x86x92Ca3(PO4)2+6H2Oxe2x80x83xe2x80x833)
Thus the acid introduced to accelerate the hydrolysis should be a dilute solution of a strong acid such as dilute hydrochloric acid or alternatively, dilute sulfuric acid or dilute nitric acid. The dilute hydrochloric acid should be heated to at least 65xc2x0 C., ideally to between 90 and 100xc2x0 C.
The invention disclosed in claims 23 through 26 of this application relates primarily to a method for processing lithium ion batteries which contain lithium hexafluorophosphate in their electrolyte. However, batteries which contain, in their electrolytes, salts comprising cations and Lewis acid ions also fall within the range of applicability.
In addition to lithium ions (Li+), the cations which may serve as salts in the electrolyte include sodium ions, potassium ions and tetraalkylammonium ions. Lewis acid ions which may serve as salts in the electrolyte include BF4xe2x88x92, PF6xe2x88x92, AsF6xe2x88x92 and ClO6xe2x88x92. The salts comprising these cations and Lewis acid ions should be heated under reduced pressure so as to effectively remove all water and oxygen before they are used as electrolytes.
This invention employs a water bath as a means of separating the salt component of the battery. The process is distinguished by comprising the following steps. In the method of processing the battery, the crushed fragments of the battery which contain the salts are immersed in water, and the salts are separated and go into an aqueous solution. A heated acid solution is added to the aqueous solution containing the salts to accelerate the hydrolysis of the Lewis acid ions. A fixative such as calcium hydroxide is added to the ion solution to fix the ions. More specifically, in the method of processing lithium ion batteries which contain lithium hexafluorophosphate in their electrolyte, the crushed fragments of the battery which contain the lithium hexafluorophosphate are subjected to a specified separation process in which heat is applied, the exhaust gases are processed and the fragments are immersed in a water bath. A heated acid solution is added to the aqueous solution containing the lithium hexafluorophosphate which has been separated into the water. The lithium hexafluorophosphate is hydrolyzed into fluorine ions and potassium ions, and a fixative such as calcium hydroxide is added to the ion solution to fix the ions.